Friday, March 1, 2013

All major intestinal helminth infections are still solely
dependent on microscopy for diagnosis. Helminth eggs are often easier to find
and identify because of their size and their distinctive morphological
features. In some cases, the helminthes
(eggs/ova) are present in sufficient quantities to be found by direct
examination of a small amount of faeces, i.e. the direct smear.

It is usually more efficient for laboratories to do a simple
concentration to avoid overlooking parasites that may be present in very small
numbers.

A modification of the direct smear procedure, the Kato-Katz
technique, is specially useful for field surveys aimed to detect schistome or
soil-transmitted nematode (Round worm, whipworm and hookworm) because it also
gives an estimation of the intensity of infection.

1.With a wax pencil or other marker, write the
patient's name or identification number and the date at the left-hand end of
the slide.

2.Place a drop of saline in the centre of the left
half of the slide and place a drop of iodine solution in the centre of the
right half of the slide (Fig .1).
(Note. Iodine wet mount preparations are most useful for protozoa, less so for helminths.)

3.With an applicator stick or match, pick up a
small portion of faeces (approximately 2 mg which is about the size of a match
head) and add it to the drop of saline: add a similar portion to the drop of
iodine. Mix the faeces with the drops to form suspensions (Fig. 2). .

4.Cover each drop with a cover slip by holding the
coverslip at an angle, touching the edge of the drop, and gently lowering the
coverslip onto the slide so that air bubbles are not produced (Fig. 3).
(Note ideal preparations containing 2 mg of faeces are uniform - not so thick
that faecal debris can obscure organisms, nor so thin that blank spaces are
present.)

Examine the preparations with the 10X objective
or, if needed for identification, higher power objectives of the microscope in
a systematic manner (either up and down or laterally) so that the entire coverslip
area is observed (Fig. 4).

When organisms or suspicicus objects are seen, switch to higher magnification
to see the more detailed morphology of the object in question.

Source: The procedure mentioned above is reproduced from Bench Aids for the Diagnosis of Intestinal Parasites published by World Health Organisation.